The invention relates to new and useful improvements in draw works use in a drilling rig.
There are many situations in which it is desirable to drive a rotating object with a hydraulic apparatus, and further to provide a braking force to the object without the use of friction braking. An example is draw works used in the oil and gas drilling industry for raising and lowering drill pipe into a borehole during drilling or workover operations.
The draw works on a drilling rig consists of a powerful winch having a large drum for storing cable. The cable is interconnected to the drill pipe support mechanism by means of a travelling block, and rotation of the drum raises and lowers the travelling block, and thus the drill pipe string. When the drill string is being raised, the draw works supports the full weight of the drill string until the slips are engaged to support the string while a section of pipe is being removed. When the drill string is being lowered, the winch is allowed to free-wheel as the drill string is dropped under the force of gravity. When a sufficient length of the drill string is thus inserted into the borehole, a brake is applied to stop the fall.
In the present practice the draw works is usually powered by an internal combustion engine or an electic motor, and the braking is a sequential operation using two different types of braking mechanisms. Although the typical draw works has a friction brake consisting of a metal band about a drum, it is not initially used since the momentum of the dropping drill string would quickly wear it out. Instead a water brake, consisting of a paddle wheel in a volume of fluid, is used to dampen, and thus slow, the fall of the drill string. Only when the drill string has been slowed sufficiently by the water brake is the band brake engaged to apply the final braking force.
It is therefore an object of the present invention to provide a draw works, or similar winch device, driven by a hydraulic mechanism.
It is another object of the present invention to provide a draw works, or other similar winch device, having an easily operable speed control.
It is a further object of the present invention to provide a draw works, or other similar winch device, in which the motive mechanism is also used for braking.
It is a yet another object of the present invention to provide a hydraulically operated draw works, or other similar winch device, whose motor also acts as a water brake.
It is still another object of the present invention to provide a hydraulic draw works, or other similar winch device, having a hydraulic braking mechanism which is not subject to cavitation.